The long term objective of this project is the development of accurate, robust and economical electrochemical sensors to be used in the life sciences and medicine. Specific aims include the design and construction of gas-sensing and esophageal pH electrodes. Electrodes will be constructed by vacuum sputtering special materials on substrates to form pH electrodes. These miniature pH electrodes. These miniature pH electrodes will be further modified to produce gas-sensing electrodes which can monitor blood gases such as carbon dioxide and ammonia. Single esophageal pH electrodes will be made by sputtering on glass substrates connected to long thin cables. Further development will lead to dry, sterilizable, combination esophageal pH electrodes. Sputtered electrodes have the combined advantages of low electrical resistance, fast response, durability and low cost. vacuum sputtering allows the manufacture of electrodes in a wide variety of shapes and sizes.